1. Field of the Invention
The present invention relates to a motor drive circuit that rotates a rotor by supplying the currents of different phases to two coils.
2. Description of the Related Art
There are a variety of types of motors available. A typical example of such motors capable of accurately determining the positions is a stepping motor which is widely in use and applicable to various types of apparatuses. For example, the stepping motor is used to focus a lens group in a camera, correct a shake, position a machine tool and so forth.
In a general stepping motor, the rotational position of a rotor is controlled by the phase difference between the currents supplied to two stator coils. Nevertheless, when the currents supplied to the stator coils are too low, the torque is too small and the synchronism may possibly be lost. In order to robustly rotate the rotor, therefore, a relatively large current is preferably supplied to the status coils.
At the same time, there is demand that the power consumed by electric equipment be minimized. Such demand is particularly strong in the field of portable devices or the like driven by batteries. Thus, a drive system capable of being driven with a lower power consumption while suppressing the loss of synchronism is in great demand.